1. Field of the Invention
The present invention relates to a centrifugal blood pump used for heart-lung machines or the like.
2. Prior Arts
In recent years, centrifugal blood pumps have begun to be used widely as blood circulation pumps for heart-lung machines or the like. In the case of a centrifugal blood pump having a structure wherein the rotation shaft of the impeller with pump vanes accommodated in the casing thereof passes through the casing, however, thrombus is apt to occur at bearings and sealing parts because of blood stagnation around the rotary sealing parts for sealing the rotation shaft of the impeller and heat generation in the rotary sealing parts. Furthermore, there is the danger of leaking blood because of incomplete operation or deterioration of the rotary sealing parts during use. By reason of these problems, such a centrifugal blood pump has a disadvantage of being incapable of operating continuously for an extended period of time.
To solve these problems, various centrifugal blood pumps have been developed, which require no sealing parts at the rotation shaft thereof. As a pump with no sealing parts, a centrifugal blood pump is known, wherein a conical impeller comprising pump vanes and a magnet means such as permanent magnets for rotating the impeller in cooperation with a magnet drive means is accommodated in the conical casing thereof having an inlet port and an outlet port, the upper and lower ends of the rotation center axis of the impeller are supported inside the casing and the impeller is rotated by a magnet drive means, such as electric coils, for generating a rotating magnetic field, disposed outside the casing, as disclosed by U.S. Pat. No. 4,507,048.
In this kind of a blood pump, a pivot is formed on the bottom end side of the rotation center axis line of the impeller thereof and this pivot is supported by a bearing, such as a watch-type jewelled bearing or the like, disposed at the central section of the upper surface of the casing's bottom wall. The shaft or pivot formed on the upper end side of the rotation center axis line of the impeller is supported by a bearing which is supported by an appropriate supporting means, such as a bar, spider or ring, just under the inlet port provided at the top section of the conical casing. In the case of the centrifugal blood pump disclosed by the above-mentioned USP, wherein both the pivots formed on the upper and lower end sides of the rotation center axis line of the impeller are supported by watch-type jewelled bearings, an adjusting means (a screw adjusting means for example) for adjusting the positional relationship between the bearing on the upper end side and the bearing on the lower end side, that is, the difference in height between the two bearings is provided.
When the pivot or shaft on the upper end side of the impeller rotation center axis line is supported by a mechanical bearing, such as a watch-type jewelled bearing as described above, it is found that the following problems are apt to occur.
Blood sucked from the inlet port collides against the bearing provided just under the inlet port positioned at the top section of the conical casing, the supporting means, such as a bar, spider or ring, for supporting the bearing, and the adjusting means for adjusting the positional relationship between the bearing on the upper end side and the bearing on the lower end side. The flow of the blood is thus disturbed by the collision, thereby causing the problem of damaged blood cells, that is, hemolysis and thrombus.
To avoid the generation of hemolysis and thrombus, the supporting means, such as a bar or the like, for supporting the bearing must be made as slender as possible. As a result, the supporting means may deform during pump operation. If such a deformation occurs, the distance between the upper and lower bearings, which was adjusted properly before operation, and the contact pressure between the impeller and the upper and lower pivots are changed, thereby hindering the impeller from rotating stably. This unstable rotation further increases the deformation of the supporting means, resulting in the breakage of the supporting means in an extreme case.
Accordingly, the above-mentioned centrifugal blood pump cannot be used continuously for an extended period of time because of the generation of hemolysis and thrombus and the unstable rotation of the impeller due to the deformation of the bearing supporting means during operation as described above.